Cultivating physical toughness

I'm looking for some two-man exercises that can be done to improve one's ability to take a hit and physical toughness. We've got a few students at our school who can't take more than one or two hits of a type that merely daze others, and they don't seem to be improving.

And what is your relationship to the students--peer, assistant instructor, instructor, head instructor, Grand Soke of Tang Soo Do?

Without knowing specifics of what kind of hits make them uncomfortable (face? head? body? appendages? With or without gear?), I would recommend hitting a heavy bag, kotekitae, and having someone strong kick a kick shield that they're holding. Sounds like sparring is too much for now.

My relationship to the students is a senior belt frequently placed in a mentoring position and with enough pull with the instructor to suggest changes to the curriculum that will be seriously considered.

If you can't take shots then maybe this isn't the hobby for you. Mostly taking shots is a mentality thing and this isn't something you can do drills to improve. If you don't have the determination to keep going after getting hit, this may not be the hobby for you.

You should spar hard contact, probably with thicker gloves and better headgear than you use now. 12oz gloves should do the trick, and I'm assuming you use those dinky little foam rubber helmets. Dash them and use boxing helmets. Then commence punching each other in the face, at least biweekly.

12oz are light for sparring. They're on the heavy side for fight gloves but they';re fight weight none the less and pretty under protective for sparring. You can really hurt someone if you're older then 12.

Most gyms want you to have 16 ouncers for sparring. Personally I wear 14's but i'm a scrawny girl (unless I know i'm going to spar someone that annoys me, then I leave on my 10's). Guys on the bigger side should probably look at 18oz or even 20.

But yeh, it's really just a matter of mentality. Maybe they'll get used to it, maybe they wont. If they can't/wont cultivate the mental toughness to continue going then martial arts are not the physical pursuit of choice for them and they might just have to accept that.